1. Field of the Invention
The present invention relates to a deckle piston compression and adjustment mechanism. More specifically, the invention relates to a deckle piston compression and adjustment .mechanism which prevents the die manifold from leaking.
2. Description of the Related Art
Coating web material with a die is a highly developed and well known field. Dies exist for coating substrates of any desirable size with a fluid. These fluids can be hot melts, water based, solvent based, one, two or multiple component based. It is common practice to coat substrates of varying width using a single die. For example, a 60 inch wide coater may be configured to coat a 50 inch wide substrate by having the die deckled 5 inches per side. The two deckles each carry a shim sized to fill the die land, thereby creating a die orifice 50 inches wide through which the coating material is extruded, as is well known in the art.
In order to adjust the position of the deckles, a prior art technique was to simply take the die apart and install the deckles and shims manually. This procedure was not only very time consuming, but hazardous if the die was hot and always creates a risk of damaging the die. As is well known in the art, dies are machined to very high tolerances, on the order of 1/10,000 of an inch. Scratches on the die land create undesirable streaks in the coating.
In order to overcome the need to take the die apart, prior art adjustable deckles were developed to allow adjustment of the coating width by moving the deckles, without the need to dismantle the die. Existing adjustable deckles either use deckles which carry O-rings or use machined steel deckles which tightly fit the die manifold. Like May Coating Technologies other competitors, applicant utilized adjustable deckles in which precision machined steel deckles were designed to fit the die manifold, being machined approximately 1/1,000 inch smaller than the size of the die manifold. These steel deckles either held one or more O-rings or seals to seal the die manifold and prevent the fluid from leaking, or relied on a close machined fit of the deckle in the manifold with no seals.
Leaking fluid is much more of a problem in die coating than in other types of dies such as plastic extruding dies, due to the much less viscous nature of many coatings. For comparison purposes water measures 1 centipoise, hot melt measures approximately 100 to 150,000 centipoise depending on the type, house paint measures approximately 750-5000 centipoise, peanut butter measures approximately 250,000-300,000 centipoise and plastic measures approximately in the range of 1-6 million centipoise. Because many desirable coating fluids, such as hot melt are much less viscous than extruded plastics they leak around seals much more readily.
Applicant has also found that prior art deckles leak under pressure. Prior art deckles also tend to seize up, making them difficult to move. Prior art deckles are also very expensive to machine and install since the tolerances need to be so close. The prior art deckles are very high maintenance, in part due to cut seals caused by imprecise machining and the build up of cured, dried, charred material cutting or tearing the seals as the seals slide over the cured, dried or charred material.
Cut seals are caused by both by imprecise machining and the build up of cured, dried or charred material in the die manifold. In actual operation the die is used at a variety of widths. When the deckles are adjusted to provide a narrower coating width the fluid in the die manifold outside the coating width comes into contact with ambient air and cures, dries or chars. When the deckles are moved back to a wider position the hardened material causes the seals to cut or tear as the seals slide over the cured, dried, or charred material. Applicant has experimented with the use of scraper bars which would scrap the hardened cured, dried or charred material out of the path of the seals, but has found that these not only do not work, but can scratch the die manifold or bind.
The entire coating industry up until now has simply lived with the need for frequent down time required to replace torn seals or leaking deckles. Up until the present invention, applicant, like others, also simply put up with a certain amount of fluid material leaking out the ends of the die manifolds. In fact, prior to the current invention it was not uncommon to find cups or other containers attached to the ends of the die manifolds to catch the leaking coating fluid.
There remains a need for an improved deckle seal mechanism which would provide a better seal than O-rings or other seals and would not tear. This improved deckle seal would not only result in higher productivity due to less down time, but it is safer since it would not require disassembly of a hot, heavy, precisely machined die.